1. Field of the Invention
The present invention relates to plural-reflector antenna systems including a main reflector, a subreflector, and a primary radiator.
2. Description of the Related Art
Japanese Laid-Open Patent Publication 2002-135042 discloses technology for lessening the deterioration of VSWR in the central vicinity of a subreflector in an antenna system. According to Japanese Laid-Open Patent Publication 2002-135042, conventional antenna systems are constituted of two reflectors, i.e., a paraboloidal main reflector and a hyperboloidal subreflector, a primary radiator, and a vertex matching section that is disposed in the central vicinity of the subreflector and is constituted from a circular-plate with a convex or concave contour. Electric waves radiated from the primary radiator are radiated into space after being reflected by the subreflector and the main reflector. In this situation, in cases where no vertex matching section is provided, electric waves radiated from the primary radiator to the central vicinity of the subreflector are directly reflected by the subreflector to the primary radiator, and the reflected electric waves deteriorate the VSWR of the primary radiator. The vertex matching section has a protruded or recessed contour, and is disposed in the central vicinity of the subreflector, in such a manner that electric waves that reenter the primary radiator after being reflected by the vertex matching section have phases opposite to those of other waves that come from the region outside the vertex matching section and reenter the primary radiator. As a result, electric waves that reenter the primary radiator are nearly cancelled out on the whole by disposing the vertex matching section; therefore, the deterioration of the VSWR is lessened.